Scavenge pumps are found in devices which include a lubricating system. These pumps are useful to propel used oil back to an oil sump or tank under certain conditions, for instance when gravity or air pressure is not sufficient to move the used oil. Oil circulating in a scavenge oil circuit, and referred to herein as scavenge oil, is usually a mix of air and oil, which mixture forms a foam-like fluid. Scavenge pumps are often required at remote locations, namely locations that are relatively far from the oil sump or tank. For instance, in the case of a gas turbine engine, a scavenge oil circuit for a bearing cavity at the rear end of the engine may require the use of a scavenge pump. Existing arrangements involving scavenge pumps use mechanical or electrical power to be provided at the remote location where the scavenge pump is located. This external power is supplied by a dedicated external line and it requires appropriate control arrangements, such as a switch or an actuated valve, thereby adding weight and complexity to the device in which the scavenge pump is provided.